Rotor assembly, in which at least one inter-claw space is sealed by the fan

ABSTRACT

The invention relates to a rotor assembly which is mounted such as to rotate around an axis of rotation (X-X′) and which comprises two magnet wheels with claws ( 10 ). The aforementioned magnet wheels are separated by an axial space and are disposed opposite one another. Moreover, each wheel ( 10 ) comprises an end shield ( 11 ) which is essentially perpendicular to the aforementioned axis (X-X′), and claws ( 12 ) extended axially from said end shield ( 11 ) towards the other wheel ( 10 ). The claws ( 12 ) of one wheel ( 10 ) are solidly connected to the end shield ( 11 ) by respective bases ( 121 ) which are separated from one another by peripheral spaces ( 13 ). The inventive assembly comprises at least one fan ( 30 ) which is positioned on an axial face of the end shield (11) of one of the wheels ( 10 ) opposite the other wheel ( 10 ), such that the fan ( 30 ) axially seals at least part of one of the peripheral spaces ( 13 ).

AREA OF THE INVENTION

The invention concerns in general rotating electrical machines inparticular automobile vehicle alternators.

More specifically the invention according to a first aspect concerns arotor assembly in particular for an automobile vehicle alternator, thisassembly being mounted rotating about an axis of rotation and comprisingtwo magnet wheels with claws separated by axial spaces and arrangedopposite each other, each wheel comprising a end shield approximatelyperpendicular to the axis and the claws extending axially from the endshield towards the other wheel, the claws of one wheel being attached tothe end shield by respective bases mutually separated by peripheralspaces, the assembly comprising at least one fan positioned on the axialface of the end shield of the one wheel opposite the other wheel.

PRIOR ART

Assemblies of this type are known from the prior art, for exampledocument EP A 0 515 259 (U.S. Pat. No. 5,270,605) and are widely used ininternally ventilated compact alternators of automobile vehicles.

OBJECTS OF THE INVENTION

One constant objective of research in the field of alternators is toreduce the noise produced by rotation of the rotor assembly.

To this end the rotor assembly of the invention, while complying withthe generic definition given in the introduction above, is essentiallycharacterised in that part of this fan axially seals at least partly oneof the peripheral spaces.

In a possible embodiment of the invention, the fan comprises a plateapproximately perpendicular to the axis and attached to the end shield,and blades projecting from the plate.

Advantageously a sealing section of the plate comes to seal axially atleast one of the peripheral spaces.

Preferably said sealing part of the plate carries an axial reliefextending from the plate between the claws.

In this case the axial relief can be shaped so as to serve as a fixingclip for the fan on the corresponding magnet wheel.

For example the plate comprises a solid part of approximately annularform.

According to an embodiment of the invention, a zone of the solid partconstitutes the sealing part.

Also the claws have radially external faces defining the diameter of therotor assembly, the solid part having an external diameter equal to orless than the diameter of the rotor assembly.

Alternatively the sealing part of the plate protrudes radially towardsthe outside from the solid part.

In this case the solid part can have a radially external edge in whichis hollowed out at least one recessed zone, the sealing part extendingfrom the base of the recessed zone.

Advantageously said sealing part is inclined axially from the solid partof the plate at the side of the claws.

In this case the fan can comprise a blade extending at least partly overthe sealing part.

In a first embodiment the fan is moulded.

In the second embodiment the fan is made of folded metal sheet.

In this second embodiment also a so-called sealing part of the platecomes to seal axially at least one of the peripheral spaces.

According to an embodiment, the plate comprises a solid part ofapproximately annular form, a zone of this solid part constituting thesealing part.

According to another embodiment, the plate comprises a solid part ofapproximately annular form, said sealing part of the plate comprising atab protruding radially towards the outside from the solid part.

In this case the tab can be inclined axially from the solid part at theside of the claws.

According to another embodiment the plate comprises support parts forthe blades cut out of the periphery of the plate, one of the supportparts constituting the sealing part.

Also the fan can comprise a second plate attached to the plate andsupporting the blades, the one plate and the second plate being able tocomprise at least one sealing part.

Alternatively the plate and the second plate each comprise at least onesealing part.

In this case the plate and the second plate can comprise respectivecomplementary sealing parts sealing the same peripheral space.

Advantageously the plate is attached to the axial face of the end shieldof the magnet wheel, the second plate being positioned on a side of theplate opposite said axial face.

Conversely the second plate can be attached to the axial face of the endshield of the magnet wheel, the plate being positioned on a side of thesecond plate opposite said axial face.

In all cases the peripheral space may be partly or totally sealed.Similarly all peripheral spaces or just some may be sealed.

In a second aspect, the invention concerns an alternator oralternator-starter of an automobile vehicle comprising a rotor assemblywith the characteristics described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will become clearfrom the description below which is provided for information and is inno way limitative, with reference to the attached drawings in which:

FIG. 1 is a perspective view of a rotor assembly according to the priorart,

FIG. 2 is a perspective view of a fan of a rotor assembly according to afirst embodiment of the invention in which the fan is moulded,

FIG. 3 is a perspective view along arrow III in FIG. 2,

FIG. 4 is a perspective view of the fan in FIGS. 2 and 3 mounted on amagnet wheel of the rotor assembly,

FIG. 5 is a perspective view along arrow V in FIG. 4,

FIGS. 6 to 9 are views equivalent to FIGS. 2 to 5 for a rotor assemblyaccording to a variant of the first embodiment,

FIG. 10 is a perspective view of a fan of a rotor assembly according toa second embodiment of the invention in which the fan is made of foldedsheet metal,

FIG. 11 is a partial cross-section view in a radial plane of a magnetwheel on which is positioned a variant of the fan in FIG. 10,

FIG. 12 is an axial view of a rotor assembly according to a variant ofthe second embodiment of the invention, and

FIG. 13 is a perspective view of the magnet wheel in FIG. 1.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 shows a rotor assembly 1 for an automobile vehicle alternatorrotating about an axis of rotation X-X′. This assembly is shrunk onto ashaft 2 and firmly attached to this in rotation about axis X-X′ bysplines carried by this shaft 2, these splines co-operating with groovesarranged in the rotor assembly 1.

The rotor assembly 1 comprises two magnet wheels with claws 10 firmlyattached to the shaft 2 and separated by an axial spacing, a hub (notshown) enclosed between the two magnet wheels 10 and an inductive coil21 wound on the hub.

The magnet wheels 10 each have the general form of a disc centred onaxis X-X′ and are arranged facing each other. Each wheel 10, as is shownin FIG. 1, comprises a end shield 11 in the form of a disc centred onaxis X-X′ and approximately perpendicular to this axis, and claws 12arranged in a circle on the outer periphery of the end shield 11 andspaced regularly along this periphery.

The end shield 11 is pierced by a central bore holding the shaft 2.

The claws 12 are made of the same material of the end shield 11 andextend axially from the end shield 11 towards the other magnet wheel 10.The two wheels 10 bear the same number of claws 12, the claws 12 of onewheel being angularly offset in relation to those of the other wheelsuch that the claws of the two wheels intermesh, a claw of one magnetwheel becoming axially engaged between two claws of the other magnetwheel.

The claws 12 (FIG. 13) of the same wheel 10 are attached to the endshield 11 by respective bases 121, these bases protruding radially froman outer edge of the end shield 11. The bases 121 are mutually separatedby peripheral spaces 13 which, perpendicular to the axis of rotationX-X′, have the general form of a ring sector. Following the periphery ofthe end shield 11, alternately a space 13 is followed by a base 121.

The claws 12 also each comprise a head, also called a tooth, of globallytrapezoid form 122, extending the base 121 axially towards the otherwheel 10.

The heads 122 have radially outer faces 123 describing a cylindercoaxial to the axis of rotation X-X′ and defining the diameter of therotor assembly 1. These faces 123 viewed in planes perpendicular to theaxis of rotation X-X′ have respective widths which shrink from the base121 towards the opposite magnet wheel 10. Here the heads 122 have a formsimilar to that described in document EP 0 515 259 to which reference ismade for further details. The heads therefore have peripheral chamfersand anti-noise chamfers 126 described below.

The rotor assembly 1 comprises at least one fan 30 attached to an axialface 111 of the end shield 11 of one of the wheels 10, said face beingturned in a direction opposite to the other wheel 10.

The base 121 (FIG. 13) is delimited from the side of the axial face 111by a straight facet 124 extending in the same plane as said axial face,an oblique facet 125 linking the straight facet 124 to the outer face123 of the head 122, and two chamfers 126 laterally framing the obliquefacet 125 and thus linking the straight facet 124 to the outer face 123.The oblique facet 125 and the chamfers 126 are inclined axially towardsthe opposite magnet wheel 10 from the straight facet 124. The chamfers126 are slightly inclined laterally towards the adjacent claws 12.

A rotor assembly 1 for an automobile vehicle alternator according to thepresent invention is substantially similar to the rotor assembly of theprior art depicted in FIG. 1, and only the fan 30, which differ, willtherefore be explained in detail below. To simplify the description, allelements of the rotor assembly 1 according to the present inventionsimilar to those of the rotor assembly of the prior art depicted in FIG.1, are designated by the same reference numerals.

According to the invention, part of this fan 30 seals at least partiallyone of the peripheral spaces 13 in an axial direction i.e. parallel tothe axis of rotation X-X′.

Here the term seal means that said fan part comes to close theperipheral space 13 on an axial side opposite the other wheel 10. Saidfan part thus extends between the two bases 121 framing the peripheralspace 13, from the one to the other.

It is positioned against the straight facets 124 of these bases or atleast extends to the immediate proximity of the straight facets suchthat the space between said fan part and the bases is very small inrelation to the dimensions of the peripheral space 13. Also said fanpart extends over the majority of the radial height of the peripheralspace 13.

The fan 30 comprises a plate 31 approximately perpendicular to axis ofrotation X-X′ and attached to the end shield 11, and blades 32protruding from the plate 31 in the direction opposite the wheel 10. Thefixing to the end shield is achieved for example by riveting and/orgluing.

In a first embodiment corresponding to FIGS. 2 to 9, the fan 30 ismoulded. It is typically made of plastics material but can also be madeof other materials.

As will be seen on FIGS. 2 and 3, the so-called sealing parts 311 of theplate 31 come to seal axially the peripheral spaces 13.

Naturally it is possible that the sealing parts 311 of the plate 31 donot seal all the peripheral spaces 13 but only some of them.

As will be seen on FIGS. 2 and 3, the plate 31 comprises a solid part312 of approximately annular form, and an edge 313 of axial orientationstanding on a radially inner edge of the solid part. The edge 313 ofannular form delimits a central opening. FIG. 4 shows that the solidpart 312 has an outer diameter equal to or less than the diameter of therotor assembly. The radially outer edge of the solid part 312, followinga radial direction, reaches the level of the oblique facets 125.

The blades 32 project axially on a face of the plate 31 opposite the endshield 11. In the embodiments in FIGS. 2 to 9, these blades have anelongated form following a longitudinally curved direction runninggenerally from the inside towards the outside of the fan. These blades32 have an outer longitudinal end stopping on the radially outer edge ofthe solid part 312.

The sealing parts 311 are formed by zones of this solid part 312, thezones being regularly spaced along the outer edge of the solid part andlying axially in the extension of the peripheral spaces 13.

Nothing separates the sealing parts 311 from the rest of the solid part312.

In a particularly advantageous manner the sealing parts 311 each bear anaxial relief 314 extending from the plate 31 between the claws 12.

On FIG. 3 it can be seen that these reliefs 314 each have the form of athin tab firmly attached to a face of the plate 31 turned towards theend shield 11 and extending from a point on this face situated radiallyremote from the outer edge of the solid part 312.

The tab comprises a first face 315 extending obliquely from the solidpart 312 axially and radially towards the outside so that a proximal endof the first face 315. which is attached to the plate 31 is radiallyspaced from the radially outer edge of the plate 31, and a second face316 extending from a distal end of the first face parallel to the axisof rotation X-X′.

The first face 315 has a slight concave curvature turned towards theaxis of rotation X-X′ and seals the space between the chamfers 126 ofthe two claws 12 framing the peripheral space in which is engaged thetab.

The second face 316 lies in the extension of the outer faces 123 of thetwo claws and here partially seals the space separating these two outerfaces over a short axial length.

Each relief 314 carries an axial reinforcing rib 317 extending from theplate 31 along and first and second faces 315 and 316. As best shown inFIG. 3, the reinforcing rib 317 is centrally located relative to thefirst and second faces 315 and 316. The faces extend axially in thedirection opposite the blades 32.

Naturally it is possible to ensure that only certain sealing parts carryaxial reliefs.

It is noted that the first face 315 of reliefs 314 expands from theplate 31 up to the second face. Viewed peripherally to axis X-X′, thefirst face has a width which is relatively smaller close to the solidpart 312 and relatively larger at the junction with the second face 316.Therefore the axial reliefs 314 can serve as fixing clips for the fan 30on the corresponding magnet wheel 10.

In an embodiment shown on FIGS. 6 to 9, the sealing parts 311 compriseaxial reliefs 314 which then have the double function namely of sealingand as a fixing clip.

In these cases zones 318 of the solid part 312 situated axially in theextension of axial reliefs 314 are recessed. These zones wouldconstitute the sealing parts 311 on FIGS. 2 to 5. These recessed zones318 are hollowed from the outer edge of the solid part 312 and each havea general U-shape. They are delimited by a base and two lateral sidesdiverging from the base up to the outer edge of the solid part 312.

The first face 315 of the axial reliefs 314 thus each extend from thebase of a recessed zone 318 and are inclined from the base towards theoutside and towards the claws 12.

Advantageously an extended blade 32 can be provided extending along thefirst face 315 of each axial relief 314. A longitudinal, radially innerextremity of this blade is situated on the solid part 312. Thelongitudinal opposite extremity of the extended blade is located at thejunction between the first and second faces 315 and 316.

Thus a centrifugal type fan as shown on FIGS. 2 and 3 can be transformedinto a helical centrifugal fan. A centrifugal fan draws the air parallelto its axis of rotation and expels the air perpendicular to this axis. Ahelical centrifugal fan draws in the air parallel to its axis ofrotation and expels the air in a direction inclined in relation to thisaxis, the angle in incline being greater than zero and less than 90°.

It is noted that in this variant embodiment, the reinforcement rib ofFIG. 3 replaced by three webs 319 forming a reinforcement box for theaxial relief 314.

A central web 319 extends parallel to the axis of rotation X-X′ from thebase of the recessed zone 318. Two lateral webs 319 link the oppositelateral edges of the central web 319, turned towards the two clawsframing the axial relief 314, to the lateral edges of the first andsecond faces, themselves turned towards the two claws.

The central web is relatively narrower than the first and second faces315 and 316 such that the lateral webs diverge from the central web tothe first and second faces. Viewed in cross-section perpendicular to theaxis of rotation X-X′, the reinforcement box therefore has trapezoidalsections, the central web of which constitutes the small base. Thelateral webs allow matching of the form of the chamfers 126 of the clawsand as a variant are extended for this purpose.

In a variant embodiment not shown, the plate 31 comprises a solid part312 of approximately annular form, the sealing parts 311 protrudingradially towards the outside in relation to the solid part 312.

In this case the solid part 312 has an outer diameter smaller than onFIGS. 2 to 9 corresponding approximately to the diameter of the endshield 11.

In a second embodiment corresponding to FIGS. 10 to 12, the fan 30 ismade of folded sheet metal. It can therefore be fixed by welding to theend shield 11. As a variant the fixing is achieved by riveting.

As before, plate 31 of this fan comprises a solid annular part 312 andblade support parts 320 cut out of the periphery of this plate.

These support parts 320 extend towards the outside from a peripheralouter edge of the solid part 312. They each have a generally triangularform, one of the sides of which constitutes a common edge with the solidpart 312 and one of the summits of which points in the radially outerdirection. The blade 32 extends along a side of the triangleapproximately between said summit pointing towards the outside and theouter edge of the solid part 312.

As in the first embodiment, a zone of this solid part 312 can constitutethe sealing part 311.

In the example embodiment shown on FIGS. 10 and 12, the sealing part 311comprises a tab 321 protruding radially towards the outside from thesolid part 312.

This tab 321 may, as shown in FIG. 10, extend in the same planeperpendicular to the axis of rotation X-X′ as the solid part 312.

It can have multiple forms: rectangular, oval, oblong etc. It can sealthe peripheral space 13 fully or partly.

The tab 321 can also be inclined axially from the solid part 312 at theside of the claws 12 as shown on FIG. 11. In this case it can have twofaces like the axial relief 314 of the first embodiment: an oblique faceof one piece with the solid part 312 and coming to seal the spacebetween the chamfers 126 of the two claws 12 between which is engagedthe tab 321, and an axial face extending the oblique face and coming toseal the space between the outer faces 123 of the claws 12.

The tab also may comprise only the oblique face.

In a variant embodiment shown on FIG. 12, the sealing part 311 cancomprise a support part 320 arranged axially in the extension of theperipheral space 13.

The fan 30 can comprise one, two or more than two sealing parts 311.

These sealing parts 311 may all be of the same type i.e. all comprisinga zone of the solid part 312, or all comprising a tab 321 or allcomprising a blade support part 320. But a single fan can also compriseseveral support parts 311 of different types without limitation of thepossible combinations.

The fan 30 can comprise a second plate 34 (FIG. 12) perpendicular to theaxis of rotation X-X′, of the same type as the plate 31 and also bearingblades 32.

The second plate 34 is positioned on the axial face 111 of the endshield 11 of the magnet wheel 10, the plate 31 being attached on oneside of the second plate 34 opposite said axial face 111. Each plate canbe fixed to the end shield 11 for example by welding, the most distantplate having passages for welding the closest plate to the end shield 11and vice versa.

The solid parts 312 of the two plates are advantageously of the samediameter. The blade support parts 320 of the second plate 34 areangularly offset in relation to the blade support parts of the plate 31such that the blades 32 of the second plate 34 intermesh between theblades of the plate 31.

Alternatively the plate 31 can be positioned on the axial face 111 ofend shield 11 of the magnet wheel 10, the second plate 32 being attachedon one side of the plate 31 opposite said axial face 111.

At least one on the plate 31 and second plate 34 comprises one or moresealing parts 311. These parts can be of any type.

It is possible that the plate 31 and the second plate 34 each compriseone or more sealing parts 311.

In this case the same peripheral space 13 can be sealed with twocomplementary sealing parts, the one carried by the plate and the otherby the second plate.

It will be clearly evident that the rotor assembly described abovepresents multiple advantages.

To seal one or more of the peripheral spaces 13 allows a reduction ofthe harmonics created by the magnet wheels and a reduction in theacoustic interaction between the rotor assembly and the statorcooperating with this assembly.

This is particularly important because the most recent fans areextremely quiet. They generate very little noise which no longer coversthe harmonics created by the magnet wheels.

It is known that the peripheral spaces separating the claws of onemagnet wheel are zones where during rotation great turbulence iscreated, with fluid detachment from the solid surface and hencesignificant pressure differences, which leads to the creation ofaerodynamic noise and hence harmonics. The sealing of these spacesachieves a significant reduction in this turbulence and in noise due torotation of the machine.

This seal is achieved in a particularly convenient and economic manneras no part is added to the rotor assembly. Elements already existing inthis assembly are used, cut or shaped differently to seal the peripheralspaces.

It is possible to achieve the seal in an asymmetrical fashion on thesame magnet wheel i.e. to seal only certain peripheral spacesdistributed irregularly or seal the peripheral spaces each in adifferent manner.

Advantageously the harmonic signals are thus distributed over a widerrange.

Also it is evident from the description above that an in-depth seal canbe obtained between the claws which increases the efficacy of thereduction of harmonics.

Finally it is possible to omit the chamfers 126 because of the presenceof these sealing parts 311. These chamfers have the same function as thesealing parts, namely to reduce the noise produced by the magnet wheelsin rotation. They are costly to machine and can affect theelectromagnetic performance of the rotor by diminishing the passage ofelectromagnetic flux in the claw. In this case the oblique facet 124 issimply extended transversely on both sides.

Although we have described a rotor assembly fitted with a single fan,this assembly can be fitted with two fans without leaving the scope ofthe invention. The two fans are fixed to the two opposite magnet wheelsand allow sealing of the peripheral spaces of the two wheels.

As will be evident, the axial reliefs 314 constitute a profiled tab soas to adapt to the inter-claw spaces.

The tabs 321, 314 allow at least partial sealing of the spaces betweenthe claws in a more effective manner than the embodiment in FIG. 12. Infact the shape of the tabs 321 and 314 is not limited by the shape ofthe blades and the function of the blades, in particular when these aremade of sheet metal.

It will be evident that the rotor according to the invention isadvantageously intended to be mounted in an internal fan alternator asdescribed for example in document EP-A 0515 259. Such an alternatorcomprises a stator surrounding a claw rotor.

The rotor is firmly attached to the shaft 2 mounted centrally inrotation via ball bearings, one of which is visible in FIG. 1, in ahousing with two parts called a front bearing shell and rear bearingshell. The bearing shells are hollow and each has a base fitted withopenings to form air inlets and a peripheral edge also fitted withopenings to form air outlets. The base of the bearing shells areglobally oriented transversely and centrally carry a ball bearing forrotational mounting of the rotor support shaft. The bases are eachextended at their outer periphery by the peripheral edge of globallyaxial orientation and with a shoulder for mounting the body of thestator carrying the coil with a plurality of phase windings, the caps ofwhich extend protruding axially on either side of the stator body belowthe openings of the peripheral edges of the bearing shells whenassembled for example with screws or stud bolts, to form the housing forthe stator and rotor. The rotor carries at least on one of its axialends a fan mounted radially below the cap concerned. The rear bearingshell carries at least one brush carrier while a pulley attached to therotor support shaft is adjacent to the front bearing shell. For theother constituents of the alternator, reference is made to the documentcited above. A rectifier bridge for example with diodes is linked to thephase windings. As a variant this rectifier bridge is shaped to form aninverter as described for example in document FR-A-2 745 444 to injectcurrent into the phase windings of the stator to cause the alternator tofunction as an electric motor in particular to start the combustionengine of the automobile vehicle, such an alternator being called analternator-starter.

In all cases when the rotor support shaft turns, the fan or fans allowcreation of an air current between the air inlet and outlet openingspassing through the caps of the stator winding.

Naturally the present invention is not limited to the embodimentsdescribed.

Thus the annular edge 313 in the form of a crown in FIG. 9 can comprisea magnetic target which in association with at least one sensor ensuresmagnetic monitoring of the rotation of the rotor as described indocument FR A 2 857 171, to which reference is made for further details,the alternator in this case being an alternator-starter.

More precisely the target can comprise a plasto-magnet in the form of acrown which is moulded onto the end shield of the fan as in FIGS. 2A and2B of the said document.

The holes, not referenced, which are seen in FIG. 9 can then serve forremoval from the mould.

Thanks to the target and the sensor, at the correct moment electriccurrent can be injected into the phase winding concerned of the statorwinding as described for example in documents FR-A-2 745 444, EP A 0 260176 and WO 01/69762.

All combinations are possible.

The invention claimed is:
 1. A rotor assembly mounted to rotate aroundan axis of rotation (X-X′) and comprising: two magnet wheels (10)separated by an axial spacing and arranged opposite each other, each ofthe wheels (10) comprising an end shield (11) substantiallyperpendicular to the axis (X-X′) and claws (12) extending axially fromthe end shield (11) towards the other wheel (10); the end shield (11) ofone of the magnet wheels comprising an axial face (111) opposite theother wheel; the claws (12) of one wheel (10) being attached to the endshield (11) by respective bases (121) mutually separated by peripheralspaces (13); and a fan (30) positioned on the axial face (111) of theend shield (11) of one of the wheels (10) opposite the other wheel (10)so as to axially seal at least partly one of the peripheral spaces (13);the fan (30) comprising a plate (31) substantially perpendicular to theaxis (X-X′) and attached to the end shield (11), and blades (32)protruding from the plate (31); the plate (31) having a sealing part(311) axially sealing at least one of the peripheral spaces (13); theplate (31) of the fan (30) comprising a substantially annular solid part(312) having a radially outer edge; the sealing part (311) comprising anaxial relief (314) in the form of a thin tab comprising a first face(315) axially inclined from the solid part (312) of the plate (31) atthe side of the claws (12) and from the axis of rotation (X-X′) so thatthe first face (315) extending obliquely between the solid part (312)and the axis of rotation (X-X′); the tab further comprising a secondface (316) extending from a distal end of the first face (315) parallelto the axis (X-X′); the axial relief (314) extending from the plate (31)between the claws (12); the claws (12) having radially outer surfaces(123) defining a diameter of the rotor assembly; the second face (316)of the tab (314) lying in the extension of the outer faces (123) of twoclaws (12) and partially sealing the space separating these two outerfaces over a short axial length; the solid part (312) is provided withrecessed zones (318) hollowed radially inwardly from the radially outeredge of the solid part (312), each of the recessed zones (318) beingdelimited by a base and two lateral sides diverging from the base up tothe radially outer edge of the solid part (312); the sealing part (311)extending from the base of the recessed zone (318).
 2. The rotorassembly according to claim 1, wherein a central web (319) extendsaxially parallel to the axis of rotation (X-X′) from the base of the ofthe recessed zone (318); wherein two lateral webs link opposite lateraledges of the central web (319) to the lateral edges of the first andsecond faces (315, 316) of the tab (314), and wherein the central web(319) is narrower than the first and second faces (315, 316) of the tab(314) such that the lateral webs diverge from the central web to thefirst and second faces (315, 316).
 3. The rotor assembly according toclaim 1, wherein the fan (30) is moulded and comprises a blade (32)extending along the first face (315) of the tab (314).
 4. Alternator oralternator-starter for an automobile vehicle, comprising a rotorassembly according to claim
 1. 5. The rotor assembly according to claim1, wherein the first face (315) of the tab (314) extends obliquely fromthe solid part (312) axially and radially outwardly and obliquely fromthe axis of rotation (X-X′).
 6. The rotor assembly according to claim 1,wherein the first face (315) of the tab (314) has concave curvatureturned towards the axis of rotation (X-X′).
 7. A rotor assembly mountedto rotate around an axis of rotation (X-X′) and comprising: two magnetwheels (10) separated by an axial spacing and arranged opposite eachother, each of the wheels (10) comprising an end shield (11)substantially perpendicular to the axis (X-X′) and claws (12) extendingaxially from the end shield (11) towards the other wheel (10); the endshield (11) of one of the magnet wheels comprising an axial face (111)opposite the other wheel; the claws (12) of one wheel (10) beingattached to the end shield (11) by respective bases (121) mutuallyseparated by peripheral spaces (13); and a fan (30) positioned on theaxial face (111) of the end shield (11) of one of the wheels (10)opposite the other wheel (10) so as to axially seal at least partly oneof the peripheral spaces (13); the fan (30) comprising a plate (31)substantially perpendicular to the axis (X-X′) and attached to the endshield (11), and blades (32) protruding from the plate (31); the plate(31) having a sealing part (311) axially sealing at least one of theperipheral spaces (13); the plate (31) of the fan (30) comprising asubstantially annular solid part (312) having a radially outer edge; thesealing part (311) comprising an axial relief (314) in the form of athin tab comprising a first face (315) axially inclined from the solidpart (312) of the plate (31) at the side of the claws (12) and from theaxis of rotation (X-X′) so that the first face (315) extending obliquelybetween the solid part (312) and the axis of rotation (X-X′); the tabfurther comprising a second face (316) extending from a distal end ofthe first face (315) parallel to the axis (X-X′); the axial relief (314)extending from the plate (31) between the claws (12); the axial relief(314) being shaped so as to serve as a fixing clip for the fan (30) onthe corresponding magnet wheel (10); the solid part (312) is providedwith recessed zones (318) hollowed radially inwardly from the radiallyouter edge of the solid part (312), each of the recessed zones (318)being delimited by a base and two lateral sides diverging from the baseup to the radially outer edge of the solid part (312); the sealing part(311) extending from the base of the recessed zone (318).
 8. A rotorassembly mounted to rotate around an axis of rotation (X-X′) andcomprising: two magnet wheels (10) separated by an axial spacing andarranged opposite each other, each of the wheels (10) comprising an endshield (11) substantially perpendicular to the axis (X-X′) and claws(12) extending axially from the end shield (11) towards the other wheel(10); the end shield (11) of one of the magnet wheels comprising anaxial face (111) opposite the other wheel; the claws (12) of one wheel(10) being attached to the end shield (11) by respective bases (121)mutually separated by peripheral spaces (13); and a fan (30) positionedon the axial face (111) of the end shield (11) of one of the wheels (10)opposite the other wheel (10) so as to axially seal at least partly oneof the peripheral spaces (13); the fan (30) comprising a plate (31)substantially perpendicular to the axis (X-X′) and attached to the endshield (11), and blades (32) protruding from the plate (31); the plate(31) having a sealing part (311) axially sealing at least one of theperipheral spaces (13); the plate (31) of the fan (30) comprising asubstantially annular solid part (312) having a radially outer edge; thesealing part (311) comprising an axial relief (314) in the form of athin tab comprising a first face (315) axially inclined from the solidpart (312) of the plate (31) at the side of the claws (12) and from theaxis of rotation (X-X′) so that the first face (315) extending obliquelybetween the solid part (312) and the axis of rotation (X-X′); the tabfurther comprising a second face (316) extending from a distal end ofthe first face (315) parallel to the axis (X-X′); the axial relief (314)extending from the plate (31) between the claws (12); the tab (314)carrying an axial reinforcing rib (317) extending from the plate (31)along the first and second faces (315, 316) of the tab (314), thereinforcing rib (317) being centrally located relative to the first andsecond faces (315, 316); the solid part (312) is provided with recessedzones (318) hollowed radially inwardly from the radially outer edge ofthe solid part (312), each of the recessed zones (318) being delimitedby a base and two lateral sides diverging from the base up to theradially outer edge of the solid part (312); the sealing part (311)extending from the base of the recessed zone (318).